Providing medical liquids in a sterile and precise manner is desirable in many instances. For example, in the production of liquid medications, accurate and sterile quantities of medical liquid may be required. One apparatus employable to provide such medical liquids is a peristaltic pump. Peristaltic pumps work to deliver medical liquids by rotating a hub connected to anvils sprung against a flexible tubing line. As the anvils rotate in relation to the flexible tubing, the tubing is compressed to occlude one section from another section and to push fluids through the flexible tubing. The anvils may be spaced a predetermined distance from one another, which, in relation to a known internal diameter of the flexible tubing, enables the displacement of and dispensing of a calculable amount of fluid.
While peristaltic pumps are operable to deliver medical liquids, peristaltic pumps suffer in that the flexible tubing may move and/or twist during operation, the flexible tubing may deform over time from repeated compression and expansion, variable inlet and outlet pressure may be experienced, pulsatile flow with undesired flow reversal may occur, and/or the spring forces associated with the anvils may degrade over time. Such factors may potentially result in the dispensing of inaccurate volumes of medical liquids. As such, systems employing such peristaltic pumps typically require calibration at the outset of each medical liquid filling procedure. For example, medical personnel typically utilize a peristaltic pump system to fill a first receptacle with an amount of medical liquid corresponding to a known degree of movement of the pump. After filling, such personnel may generally compare such filled amount to a desired fill amount, and may often adjust the peristaltic pump to calibrate the system. Thus, time and/or materials may be spent in the calibration of a peristaltic pump. The tubing deformation may also lead to seepage around the anvils, thereby leading to cross-flow between the various sections of the tubing.
Peristaltic pumps also are limited by the intake speed of rotation. As the hub of the peristaltic pump is rotated, a pressure differential is created at both the inlet and outlet of the pump. These inlet and outlet pressures are generally tied to one another as the rotation rate of the hub relates to both the inlet and outlet pressures. As may be appreciated, the operable inlet pressure may be limited by the vapor pressure of the liquid being dispensed. If the inlet pressure is too high in relation to the vapor pressure of the liquid, a portion of the liquid may evaporate upon intake, which is undesirable for many reasons (e.g., the dispensing of inaccurate liquid volumes). Correspondingly, the outlet pressure, and thus the dispensing rate, is limited by the operable inlet pressure, which may be substantially less than the operable outlet pressure, which may not be limited by the vapor pressure of the liquid. Thus, the maximum rate of fluid flow speed may be substantially less than desired due to the inherent tying of the inlet pressure to the outlet pressure in the peristaltic pump.